Hydrostatic transmission hydraulic control and single lever for operating same

ABSTRACT

Hydraulic control for two hydrostatic transmissions driving a vehicle. Straight-line movement of certain parts of the hydraulic control moves the vehicle in forward and reverse. Angular movement of certain other parts of the hydraulic control turns the vehicle. A single joy stick is directly connected with the first set of parts, and indirectly connected with the second set of parts. One type of movement of the joy stick causes the vehicle to move in forward and reverse, and another type of movement of the joy stick brings about turning of the vehicle.

United States Patent [is] 3,6

Chatterjea [451 July 18, 1972 s41 HYDROSTATIC TRANSMISSION 2,766,834lO/l956 Boyer 80/648 HYDRAULIC CONTROL AND SINGLE 2,182,459 l2/l939Vickers..... LEVER FOR OPERATING SM 3,306,385 2/1967 Kempson l 80/648[72] Inventor: Prohir K. Chatterjea, Evanston, Ill. Primary ExanunrBenjamin Hersh u H I C Amlsranr Examiner-John A. Pekar [73] Asslgnee'cago, Attorney-Floyd B. Harman [22] Filed: Sept. 2, I970 [57] ABSTRACT[2]] Appl. No.: 69,019 Hydraulic control for two hydrostatictransmissions driving a vehicle. Straight-line movement of certain partsof the hydraulic control moves the vehicle in forward and reverse.Angular S 18w 12 movement of certain other parts of the hydrauliccontrol turns the which A single joy stick is directly conncced with he[58] Field ol Search ..l80/6.48, 6.3, 137/596, 625.23 first Sc of pans,and indirectly connecmd with the second set [56] defences GM of parts.One type of movement of the joy stick causes the vehicle to move inforward and reverse, and another type of n- STATES pATENTS movement ofthe joy stick brings about turning of the vehicle.

3,540,220 1 H1970 Lauck 180/648 UX [2 Chill, 8 Dnwlngflgures L P n 123IEJ .fUlc 2 7 100 101 10 "14171114 'IIIIIIIIIA '11 YIIIIIIIIII. VIIIIIIMPatented July 18, 1972 3,677,362

5 Sheets-Sheet l Patented July 18, 1972 3,677,362

3 Sheets-Sheet 5 w 3w QM R S a m JR w) Jfi um. mm R E mut ws ma AWNI-IYDROSTATIC TRANSMISSION HYDRAULIC CONTROL AND SINGLE LEVER FOROPERATING SAME This invention relates to a hydraulic control. Morespecifically, the invention relates to a hydraulic control that iscompact and unitary and capable of being operated by a single lever.

It is known to drive a crawler or track-laying tractor in forward andreverse and to steer the same by two separate hydrostatic transmissionsacting against two separate drive mechanisms, one at one side of thetractor and the other at the other side. For straight-line movement ofthe tractor in forward or reverse, the two drive mechanisms are drivenat the same speed in the same direction. For turning, one drivemechanism is slowed, stopped, or reversed.

In many installations, it is advisable to employ a hydraulic control forthe hydrostatic transmissions in a crawler tractor. It is desirable tooperate the hydraulic control from a single member or lever.

According to the present invention, a hydraulic control of the abovetype has been provided, which is simple, compact, and unitary and can beoperated from a single lever.

More particularly, the control is for a tractor vehicle in which twodrive mechanism are driven at the same speed in a given direction forstraightforward movement of the vehicle, at the same speed in theopposite direction for straight rearward movement of the vehicle, and atspeeds in opposite directions or with a speed differential in the samedirection to execute power turns in the steering of the vehicle; and inwhich two hydraulic actuators control the direction of drive of thedrive mechanisms by the algebraic signs of the differences of thehydraulic pressures applied to the actuators, and con trol the speeds ofthe drive mechanisms by the amounts of said differences. I accordinglyprovide, in combination with the actuators, a tiltable joy stick and atranslatory and rotary bipartite valve operatively related together toafford manual control over an hydraulic pressure differential applied tothe actuators; the bipartite valve having a direction part with slidablyrelated pressure differential creating elements, the actuators beingconnected in the output of the elements and responsive to the signs ofthe differences of the hydraulic pressures applied thereto by theelements; the bipartite valve further having a steering part withrotatably related pressure differential creating members, the actuatorsbeing connected in the output of the members and responsive to theamounts of differences of the hydraulic pressures applied thereto by themembers; means supporting the joy stick and bipartite valve in theoperative relationship described enabling rightward and leftward tiltingof the joy stick to turn the members of the steering part in twodirections of rotation; and means supporting the joy stick and bipartitevalve in the operative relationship described enabling forward andrearward tilt of the joy stick to slide the elements of the directionpart in two directions of translation.

IN THE DRAWINGS FIG. I is a perspective view of a direction unit for avehicle, a steering unit, and a joy stick governing the unit;

FIG. 2 is a longitudinal sectional view of the direction and steeringunits;

FIG. 3 is a longitudinal horizontal sectional view of the direction andsteering units;

FIG. 4 is a transverse sectional view through the steering unit taken onthe line 4-4 of FIG. 2;

FIG. 5 is a perspective view, partially broken away in section, of asleeve of the steering unit;

FIG. 6 is a diagrammatic view of the direction and steering units andthe hydraulic controls therefor;

FIG. 7 is a schematic developed view of portions of the steering unit;and

FIG. 8 is a view similar to FIG. 7, but with the parts in a differentrelative position.

As shown in FIGS. 1 and 6, a direction unit 20 and a steering unit 21are operated by ajoy stick to control power units 23 and 24 forpositioning two swash plates (not shown) of two swash plate type pumps(not shown) for driving two drive mechanisms (not shown) for a vehicle,for example, the power unit 23 controlling the swash plate of the pumpfor the lefthand drive mechanism, and the power unit 24, the swash plateof the pump for the right-hand drive mechanism. Specifically, the plateangle of the swash plate is thus controlled to vary pump displacement.Similarly, if a tilting head type hydrostatic pump is employed, the tiltangle of the head is so controlled to vary pump displacement.

As shown in FIG. 6, a control pump 25 driven by the vehicle enginesupplies hydraulic fluid through an antistall device 26 and a line 27 tothe direction unit 20 and thence through the steering unit and a line 28to a drain 29. Two hydraulic lines 30 and 31 connect the direction unit20 with the steering unit 21. Two hydraulic lines 32 and 33 connect thesteering unit 21 with opposite ends of a control valve 34 for the powerunit 24 for the right-hand drive mechanism. The hydraulic lines 35 and36 connect the steering unit 21 with opposite ends of a control valve 37for the power unit 23 for the left-hand drive mechanism of the vehicle.

Forward or reverse movement of the joy stick 22 in the direction of thearrows FORWARD" and "REVERSE" shown in FIG. 1 causes the direction unit20 to act through the control valves 34 and 37 against the power units23 and 24 and thereby actuate the drive mechanisms for forward orreverse movement of the vehicle. Rightward or leftward movement of thejoy stick 22 in the direction of the arrows LEFT TURN" and RIGHT TURNacts through the direction unit 20 to cause the steering unit 21 tooperate through the control valves 34 and 37 and thereby make the powerunits 23 and 24 actuate the drive mechanisms for a turn of the vehicleto the left or to the right.

As shown in FIGS. I, 2, and 3, the direction unit 20 comprises amanually adjustable member 38 and an outer member 39 tightly enclosingthe same. The inner member 38 is mounted in the outer member 39 forreciprocal movement along the axis of the inner member 38 and forangular movement or rotation about its axis. The inner member 38protrudes from the outer member 39 and terminates in a bifurcated end390, which receives, and is pivotally connected to, an intermediateregion of the joy stick 22 by a pin 40. The joy stick 22 has a lowerbifurcated end 40a which straddles a fixed rod 40b. In longitudinalmovement of the inner member 38, the joy stick 22 pivots about the fixedrod 40b. During angular movement of the inner member 38, the joy stick22 pivots about the axis of the inner member and its lower end 40a movesalong the fixed rod 40b.

The inner member 38 has at an intermediate region located within theouter member 39, a wide external annular groove 41, and two narrowshallow external helical grooves 42 and 43 which are formed in portionsof the inner member 38 beyond the ends of the wide groove 41 and extendin opposite directions from the wide groove 41 to a narrow annularexternal peripheral groove 44 and to a shoulder 45, respectively. Theshoulder 45 is located at the juncture of a reduced extension 46 of theinner member 38 with the balance thereof. The narrow groove 44 isdisplaced from the wide groove 41 axially of the inner member 38 in theopposite direction to the shoulder 45 and is connected by radialopenings 47 with a longitudinal axial passage 48 in the inner member 38which has a closed end adjacent the bifurcated end 39a of the innermember 38 and an open end at the free end of the reduced extension 46 ofthe inner member 38. Radial passages 49 which are formed in the reducedextension 46 adjacent the shoulder 45 connect the passage 48 with theexterior of the extension 4 The outer member 39 of the direction unit 20has a narrow annular internal peripheral groove 50 located so as to bein communication with the wide groove 41 on the inner member 38 in itsvarious longitudinal positions. The supply line 27 is connected to anopening 51 formed in the outer member 39 in communication with thenarrow groove 50. The outer member 39 has a narrow annular internalperipheral groove 52 which is spaced from the narrow groove 50 along theaxis of the inner member 38 and is adjacent the narrow groove 44 on theinner member 38. The outer member 39 also has a narrow annular internalperipheral groove 53 which is spaced from the groove 50 in the oppositedirection to the groove 52, and is adjacent the shoulder 45 on the innermember 38.

The steering unit 21 comprises an inner member or rotor 54, a sleeve 55embracing the inner member 54, and a casing section 56, in which thesleeve 55 is attached, and which is im tegral with the outer member 39of the direction unit 20. The inner member or rotor 54 is keyed so as torotate with the inner member 48 of the direction unit by means of twoballs 57 which engage axial grooves 58 formed in a central axial opening59 in the rotor 54. The balls 57 are lodged in openings formed in thereduced extension 46 of the inner member 38. The inner member or rotor54 is held against axial movement in the sleeve 55 by means ofa cover orend plate 60 secured to the casing section 56 and by an annular disc 62which rests against an annular shoulder 63 formed in the easing section56 and has a central opening large enough to pass the reduced extension46 on the inner member 38 of the direction unit 20 but not large enoughto pass the balls 57 lodged in the reduced extension 46. The drain line28 is connected to an opening in the end plate 60.

As previously described with reference to FIG. 6, lines 30 and 31connect the direction unit 20 with the steering unit 21. At thedirection unit 20, the lines 30 and 31 are connected with the annulargrooves 52 and 53, which constitute take-off openings. As shown in FIGS.2 and 4, the line 30, which is connected to the annular groove 52, isactually composed of a passage 64 extending in the outer member 39 ofthe direction unit 20 from the annular groove 52, a passage 65 whichextends from the passage 64 and is formed by a groove in a bottom plate66 attached to the outer member 39 and the adjacent surface thereof, ashort passage 67 in the casing section 56 of the steering unit 21 incommunication with the passage 65, and an opening 68 in the sleeve 55 inregistry with the passage 67. As shown in FIGS. 3 and 4, the line 3!which is connected with the annular groove or take-off opening 53, isactually composed of a passage 69 extending from the groove 53 in thejuncture of the casing section 56 of the steering unit 21 with the outermember 39 of the direction unit 20, a passage 70 in the casing section56 connected with the passage 69, an opening 71 in the passage 70, andan opening 72 formed in the sleeve 55 in registry with the opening 71.

As shown in FIGS. 2 and 4, the outer surface of the inner member orrotor 54 has four arcuate segments 73a, 73b, 73c, and 73d, which engagethe interior of the sleeve 55 and are spaced from one another by fourother surface segments 74 which are planar and are spaced from theinterior of the sleeve 55 so as to form therewith four chambers 74a,74b, 74c, and 74d. The inner member or rotor 54 and the sleeve 55 havean appreciable length or axial dimension. As shown in FIGS. 2, 4, 7, and8, each of the arcuate segments 73a, 73b, 73c, and 73d is provided witha small shallow groove 75a, 75b, 75c, or 75d which extends for asubstantial portion of the length of the inner member 54 between thesides of the arcuate segment 73. Each groove 75a, 75b, 75c, or 75d isvery generally parallel to the axis of the inner member 38, althoughextending somewhat therearound, because its ends are at the sides of thearcuate segment 73. Since the inner member 54 has appreciable length, aspreviously stated, and each groove 75a, 75b, 75c, or 75d extends for asubstantial portion of the length of the inner member 54, also aspreviously stated, each groove has an appreciable length. A crosspassage 76 in the inner member 54 extends between two opposed surfacesegments 74 so as to interconnect chambers 74b and 74d. A cross passage77, which is separate from and unconnected with the cross passage 76,extends through the inner member 54 between the two remaining surfacesegments 74 so as to interconnect chambers 74a and 740.

As shown in FIGS. 4, 5, 7, and 8, the sleeves 55 has four longitudinalslots 78, 79, 80, and 81 which are of appreciable length, extendparallel to the axis of the inner member 38 of the direction unit 28,and are generally coextensive with grooves 75a and 75 b in surfacesegments 73a and 73b of inner member 54. Thus; slots 78 and 79 arecapable of overlapping or intersecting the groove 75a; and slots and 81,the groove 75b.

As shown in FIGS. 4 and 6, slots 78, 79, 80. and 81 constitute take-offopenings of the steering unit 2| and are connected respectively withlines 32, 36, 35, and 33, portions of which are formed by passages 82,83, 84, and 85, respectively, in the casing section 56 of the steeringunit IL IN NEUTRAL, VERTICALLY DISPOSED Again, with reference to thedirection unit 20, and as shown in FIGS. I, 2, 3, and 6, the hydraulicfluid in the wide groove 41 of the inner member 38 and in the ends ofthe helical grooves 42 and 43 thereon adjacent the wide groove 4I is atsource pressure or pump pressure as produced by the enginedriven pump25. When the joy stick 22 is positioned in neutral as shown, midwaybetween forward and reverse, drain pressure exists in the grooves 52 and53in the outer member 39 of the direction unit 20, because in thisposition the grooves 52 and 53 are at the groove 44 and the shoulder 45,which are at drain pressure, because of being connected with the drainline 28 through the openings 47 and 49 and passage 48 in inner member 38and the end plate 60.

Since drain pressure exists in grooves 52 and 53, and lines 30 and 31,respectively, connect these grooves with chambers 74a and 74b in thesteering unit 2i, drain pressure exists in chambers 74a and 74b. Sincechambers 74a and 74b are connected with chambers 74c and 74d,respectively, by passages 76 and 77 in the inner member 54 of thesteering unit 2], drain pressure also exists in the chambers 74c and74d. Thus, lines 32, 36, 35, and 33 are all at the same pressure,namely, drain pressure. Since lines 32 and 33 are at the same pressure,valve 34 is closed, and power unit 23 is kept from starting the drive ofthe right-hand drive mechanism of the vehicle. Similarly, since drainpressure is in lines 35 and 36, valve 37 is closed, and the power unit23 is prevented from staring the drive of the left-hand drive mechanism.

STRAIGHT AHEAD OPERATION Assume now the vehicle is to be drivenforwardly in a straight line. The joy stick 22 while extending straightup midway between "RIGHT TURN" and LEFT TURN, is moved to the right asviewed in FIG. I in the direction of the arrow FORWARD." The innermember 38 of the driving unit 20 is moved to the right as viewed inFIGS. 2, 3, and 6 of the position of these figures, with the result thatthe shoulder 45 on the inner member 38 is moved somewhat to the right ofthe groove 53 in the inner member 38, which groove in effect moves alonghelical groove 43.

Since the groove 53 is now at some intermediate point in the length ofthe helical groove 43, the pressure in groove 53, line 31, and chambers74a and 74c is at some increased level between drain pressure and sourcepressure. At the same time, the groove 52 in the outer member 39continues to overlap groove 44 on the inner member 38, in spite ofrelative shifting of these grooves, and so drain pressure continues toexist in groove 52, line 30, and chambers 74b and 74d. Since the joystick 22 is positioned between RIGHT TURN and LEFT TURN, as aforesaid,the inner member or rotor 54 of the steering unit 21 is positioned, byvirtue of its connection with the joy stick 22 through the inner member38 of the direction unit 20 and the balls 57 in the extension 46thereof, in the position of FIG. 6, in which groove 78 is overlapped bychamber 74a, grooves 79 and 80 by chamber 74b, and groove 81 by chamber74c. Since an intermediate pressure exists in chambers 74a and 740, italso exists in grooves 78 and 81 and lines 32 and 35. Since drainpressure exists in chamber 74b, it also exists in grooves 79 and 80 andlines 36 and 33.

Since line 33 continues at drain pressure, and line 32 is now at thehigher intermediate pressure, the valve 34 is opened in a way to bedescribed later and causes piston 86 of the power unit 24 to move incylinder 87 thereof to the left as viewed in FIG. 6 for producing aforward drive of the right-hand drive mechanism of the vehicle.Similarly, since line 35 is at the increased intermediate pressure, andline 36 continues at the drain pressure, valve 37 is opened in such away as to move piston 86 of power unit 23 in cylinder 87 thereof to theright as viewed in FIG. 6, causing the forward drive of the left-handdrive mechanism of the vehicle.

When the left-hand and right-hand drives of the vehicle reach the speedcorresponding to the displacement of the joy stick 22 forward from theneutral position, movement of the pistons 86 in the cylinders 87 of thepower units 23 and 24 is stopped by closing of the valves 34 and 37 dueto increase in pressures in lines 88 to those in lines 32 and 35, whichincrease in pressure is caused by adjustment of feedback devices 89 bythe shifting of pistons 86 of power units 23 and 24. Details of thepower units 23 and 24, valves 34 and 37, and the feed-back devices 89will be provided later in the specification.

Let us again consider straight-ahead forward drive of the vehicle, thistime with reference to the developed view of FIG. 7. This view isobtained by cutting the surface of the inner member or rotor 54longitudinally at the top flat segment 74 at the chamber 74d, spreadingsaid surface out flat, and superimposing in phantom the slots 78, 79,80, and 81 of the sleeve 55, The lines 30, 31, 32, 33, 35, and 36, andthe chambers 74a, 74b, 74c, and 74d.

Line 31 is at an increased pressure intermediate drain pressure andsource pressure, and the line 30 continues at drain pressure, because ofdisplacement of the inner member 38 of the direction unit to the rightas viewed in FIGS. 2, 3, and 6 from the neutral position shown in thesefigures. The increased pressure in line 31 is also present in line 32,because of the connection of these lines through the chamber 74a, slot78, and passage 82. The groove 750 does not reduce the pressure in line32 below that in line 3!, because, as shown in FIG. 7, the chamber 740is directly connected with the slot 78 and opening 82 and is connectedwith the groove 750 only at the end thereof directly adjacent thechamber 74a. The increased pressure in line 31 also exists in line 35,because these lines are connected with one another through the chamber740, cross passage 77, chamber 74c, slot 81, and opening 85. The groove75b has no effect upon the pressure in the line 35, because the slot 81and opening 85 are directly connected with the chamber 74c, while beingconnected with the groove 75b only at the end thereof connected with thechamber 740. The drain ressure, continuing in line 30, is also presentin lines 33 and 36, because lines 33 and 36 are connected with the line30 in a direct way through the chamber 741:, slots 79 and 80, andopenings 83 and 84, the connection of the lines 33 and 36 with thegrooves 75a and 75b being only at the ends thereof opening into thechamber 74b. Thus, the lines 32 and 35 are at the same increasedpressure intermediate drain pressure and source pressure, namely, drainpressure, with the result that the left-hand and right-hand drivemechanisms of the vehicle are driven in a forward direction at the samespeed and produce straight-ahead forward movement of the vehicle.

RIGHT TURN If now the vehicle is to be turned to the right, the joystick 22 is manipulated so as to move the inner member 38 of thedirection unit 20 so as to produce clockwise movement of the innermember or rotor 54 of the steering unit 21 as viewed in FIGS. 4 and 6.Clockwise movement of the inner member 54 results in relative shiftingof the slots 78, 79, 80, and 81 and openings 82, 83, 84, and 85 to theright as viewed in FIGS. 7 and 8 from the position of FIG. 7 to that ofFIG. 8. Thus, as seen in FIG. 8, the slots 78 and 80 are moved out ofoverlapping relationship with the chambers 74a and 74b, respectively,and thus out of direct connection therewith. Now the slots 78 and 80 areconnected with the grooves a and 75b, respectively, at intermediateregions of their lengths. It must be understood that there is a drop inpressure along the lengths of the grooves 75a and 75b, because thesegrooves are connected at one end to the chambers 74a and 740 at theintermediate pressure and at the other end to chamber 74b at the drainpressure, which is, of course, the lower pressure. Thus, there are adecrease in the pressure in slot 78 and the line 32 connected therewithfrom the intermediate pressure in line 31 and chamber 74a toward drainpressure, and an increase in the pressure in slot and the line 33connected therewith from drain pressure toward the intermediate pressurein chamber 740 and line 31.

Since the lines 32 and 33 are connected with the valve 34, the pressuredecrease in line 32 and pressure increase in line 33 act through thevalve 34 and power unit 24 to slow the speed of the right-hand drivemechanism of the vehicle, stop it, or reverse it, depending on whetherthe new pressure in line 32 continues greater than, is equal to, or islower than, the new pressure in line 33. Clockwise movement of the innermember or rotor 54 of the steering unit 21 has no effect on thepressures in the lines 35 and 36 and thus enables the leh-hand drivemechanism of the vehicle to continue in the same forward speed, becauseclockwise movement of the inner member 54 does not disturb the directconnection of the slots 79 and 81 with the chambers 74b and 74c,respectively, the slots 79 and 81 merely moving transversely of thechambers 74b and 74c away from the sides thereof, as will be evidentfrom the comparison of FIG. 7 with FIG. 8. Since the left-hand drivemechanism of the vehicle continues at the same forward speed, and theright-hand drive mechanism is slowed, stopped, or reversed, the vehicleis turned to the right.

LEFT TURN When the vehicle is to be turned to the left, the joy stick 22is manipulated so as to move the inner member 38 of the direction unit20 so as to cause counterclockwise movement of the inner member or rotor54 of the steering unit 21 as viewed in FIGS. 4 and 6. This results inrelative shifting of the slots 78, 79, 80, and 81 to the left of theposition indicated in FIG. 7. This new position of the slots is notshown, but can be understood by picturing the reverse of the rightwardshift illustrated in FIG. 8. With leftward movement of the slots, thelines 32 and 33 continue at the intermediate pressure of line 31 and atthe drain pressure of line 30, respectively, because the directconnection of the slots 78 and 80 with the chambers 74a and 74b,respectively, continues, since the slots 78 and 80 are merely moved outof overlapping relation with the sides of the chambers 74a and 74btoward the middle regions thereof. Since there is no change in pressurein lines 32 and 33, the righthand drive mechanism of the vehiclecontinues at the same forward speed. Slots 79 and 81, on the other hand,are moved away from the chambers 74b and 74c and become connected withintermediate regions of the grooves 74a and 74!). Thus the pressure inslot 79 and line 36 connected therewith is increased from drain pressuretoward the intermediate pressure existing in chambers 74a and 740 andline 31 and the pressure in slot 81 and line 35 connected therewith isreduced from the intermediate pressure in line 31 toward the drainpressure. Thus depending on whether pressure in line 35, though reduced,stays greater than that in line 36, becomes equal to it, or decreasesbelow it, the left-hand drive mechanism of the vehicle is slowed,stopped, or reversed. Consequently, the vehicle is turned to the left.

Only the two grooves 744 and 74b and the three chambers 74a, 74b, 74ccontrol the pressures in the slots 78, 79, 80, and 81 and thus the lines32, 36, 33, and 35 connected therewith, respectively. The remaining twogrooves 75c and 75d and the chamber 74d are not directly involved incontrol of pressures in the aforesaid slots and lines; instead, theyprovide a balance in the relationship of the inner member or rotor 54with the sleeve 55 surrounding it. Thus, the chamber 74d has the samepressure as the chamber 74b, because of the cross passage 76 connectingthese chambers. The chamber 74c has the same pressure as the chamber744, because of the connecting cross passage 77. The arcuate segments73a, 73b, 73c, and 734 on the inner member 54 have the same widths andthe grooves 75a, 75b, 75c, and 75d have the same lengths, widths, anddepths. Arcuate segments 73a, 73b, 73c, and 73d are equally spaced fromone another about the inner member 54. Thus, the inner member 540 iscentrally mounted in the sleeve 55 and has the same clearance at allarcuate segments.

A significant feature of the present invention is that each of grooves75a, 75b, 75c, and 75d is of appreciable length so that the reducedorifices formed by these grooves and the adjacent inner surface portionsof the sleeve 55 are also of appreciable length. Moreover, thesegrooves, although extending somewhat about the axis of rotation of theinner member 54, extend rather generally parallel to the axis. Thus,reliable proportional control of pressure gradient in the orificesformed by the grooves 75a, 75b, 75c, and 75d is achieved with a limitedangle of incremental rotation of the inner member 54. The grooves are ofappreciable length, although being four in number and formed on arcuatesegments 73a, 73b, 73c, and 73d of limited peripheral extent, becausethe inner member 54 on which the grooves are formed has an appreciablelength or axial dimension. It is also of significance that the grooves75a, 75b, 75c, and 75d are connected with the lines 32, 36, 35, and 33through the slots 78, 79, 80, and 81, which are also of appreciablelength and extend parallel to the axis of the inner member 54. Thus, asthe inner member 54 is turned clockwise or counterclockwise for steeringof the vehicle, the grooves 750 and 75b are always connected with theslots 78, 79, 80, and 81, and the regions of the grooves 75a and 75bconnected with the slots shifts along the grooves as the inner member 54is turned. This is evident from a comparison of FIGS. 7 and 8.

Because the grooves 75a, 75b, 75c, and 750', are long and slightlyhelical and cooperate with long longitudinal slots 78, 79, 80, and 81,and the grooves and slots are on a long inner member 54 and a longsleeve 55, the grooves and slots can function by relative rotation ofthe inner member and the sleeve. Since steering unit 21 functions byrelative rotation, because of its grooves 750 and 75b and slots 78-81,and since the direction unit 20 functions by relative longitudinalmovement of its members 38 and 39, the joy stick 22 operates by onemotion, namely, that of swinging about fixed rod 40b, to adjust thedriving unit 20, and by another motion, namely, that of pivoting aboutthe axis of inner member 38, to adjust the steering unit 2I. Since therotor 54 and sleeve of steering unit 21 are held against relativelongitudinal movement, and relative rotation of the members 38 and 39 ofthe driving unit 20 has no effect on the driving unit, the driving unitis directly connected with the joy stick 22, and the steering unit isdirectly connected with the driving unit and thus with the joy stick.Thus, a unitariness of construction is achieved.

As shown in FIG. 6, each of the power units 34 and 37 comprises ahousing 90 and a valve spool 91 which is movably mounted therein and isprovided with outer lands 91a and a central land 91!). The housing 90has a central bore 92 at which five annular grooves are formed. Themiddle groove is connected to a supply line 93 leading from a source ofhydraulic pressure fluid. The end grooves are connected to drain lines94. The two remaining grooves are connected to delivery lines 95 and 96leading to opposite ends of the cylinder 87 of the power unit 23 or 24.Beyond one end of the housing bore 92 a chamber 97 of relatively largediameter is located to which the line 33 or 36 for the valve 34 or 37 isconnected. The housing 90 has beyond the chamber 97, a chamber 98 ofrelatively small diameter to which the line 88 leading to the feed-backdevice 89 is connected. Beyond the other end of the central bore 92, Thehousing 90 has a chamber 99 of relatively large diameter to which theline 32 or 35 for the valve 34 or 37 is connected. Beyond the chamber99, the housing 90 has a chamber I of relatively small diameter to whicha line 101 is connected leading to the feed-back device 89. Pistons 101aand IOIb are mounted in the chambers 98 and 100, respectively, andproject into engagement with reduced end portions 101C ofthe valve spool91.

FEED BACK Each of the feed-back devices 89 comprises an outer member I02and an inner member 103 movably mounted therein. The inner member I03has an annular peripheral groove 104 and two narrow shallow helicalgrooves 105 and 106 extending from the ends of the groove 104 to theends of the inner member 103. The outer member 102 has an internalannular peripheral groove 107. The grooves 104 and 107 are wide enoughto remain in communication with one another in various longitudinalpositions of the inner member 103. The outer member 102 has two internalannular peripheral grooves 108 and 109, to which the lines 88 and 101,respectively, are connected, and which are positioned beyond, at, orwithin the ends of the inner member 103, depending on its longitudinalposition. A coil spring 110 acts between a closed end of the outermember 102 and the adjacent end of the inner member I03 to maintaincontact between the other end thereof and an enlarged end 111 secured toone end of a rod 112 which is attached to and extends through the piston86. The ends of the outer member 102 are connected to drain lines 113.The groove 107 in the outer member 102 is connected by a supply line 114connected to a supply line 115 leading to the engine-driven pump 25. Thepressure in the lines 88 and 101 and in the chambers 98 and 100 of thecontrol valve 34 or 37 connected thereto are dependent on the positionof the inner member 103 of the feedback device with respect to the outermember 102. The grooves 104 and 107, being connected to the pump 25 bythe lines 114 and 115, are at source pressure or pump pressure. Theinner ends of the helical grooves 105 and 106 adjacent the groove 104are likewise at source or pump pressure. The chambers or spaces in theouter member 102 of the feed-back device 89 beyond the ends of the innermember 103 are at drain pressure, as are the ends of the helical grooves105 and 106 at the ends of the inner member. Hydraulic fluid flows fromthe inner ends of the helical grooves 105 and 106 to the outer endsthereof and drops in pressure along the grooves, because they are narrowand shallow and offer considerable resistance to flow of the hydraulicfluid.

As previously stated, positioning of the inner member 38 of thedirection unit 20 for forward drive of the vehicle involves moving suchinner member to the right as viewed in FIG. 6, and this action resultsin increase in pressure in line 31 and thus in lines 32 and 35. At thesame time, the pressure in line 30 and lines 33 and 36 remain at drainpressure. Because lines 32 and 35 increase in pressure and lines 33 and36 stay at the same pressure, chambers 99 of valves 34 and 37 increasein pressure while chambers 97 stay at their same pressure. The result islefiward movement of valve spool 91 of valve 34 and rightward movementof valve spool 91 of valve 37, connection of line 96 with supply line93, connection of line 95 with drain line 94, rightward movement ofpiston 86 of power unit 23 and leftward movement of piston 86 of powerunit 24. Consequently, inner member 103 of feed-back device 89associated with power unit 23 moves to the right and the inner member103 of the outer feed-back device 89 moves to the left. The result isthat the pressure in the line 88 at each feedback device 89 isincreased, because the grooves 108 in the outer members 102 of thefeed-back devices 89 connected with lines 88 move, relatively speaking,within the ends of the inner members 103 and thus are subjected to someincreased pressure existing at some intermediate point in the helicalgrooves 105, which pressure is higher than the drain pressure beyond theends of the inner members 103.

The pressure increase in lines 88 and the chambers 98 in the outer valvemembers 90 connected to these lines causes pistons 101a, mounted in thechambers 98 and engaging the end portions 101C ofthe inner members 91,to return the inner members 91 to the position of FIG. 6, in which lands91a and 91b on the inner members 91 block the supply line 93, the drainlines 94, and the lines 95 and 96 leading to the cylinders 87 of thepower units 23 and 24. Since lines 95 and 96 are blocked, the positionsof the pistons 86 in the cylinders 87 are fixed, and as a result thespeeds of the drive mechanisms of the vehicle are set.

The antistall device 26 mentioned at the beginning of the descriptionforms no per se part of the present invention. But for sake ofcompleteness, it is described as follows. This device comprises acylinder 116, a piston 117, a coil spring 119, a piston 120 controllableby a throttle 121, a line I22 leading to a closed end of a cylinder 116from a region at the delivery side of the pump 25 ahead of a restrictionI23, and a line 124 connected between a delivery line 125 of the pump 25and a region of the cylinder 116 between the pistons 117 and 120. Thepiston 117 has a reduced middle region 1250, two diametrally opposedlongitudinal grooves 125b extending from one end of middle region 1250with a depth progressively decreasing to zero, and two diametrallyopposed longitudinal grooves 125c extending from the other end of middleregion 125a with a depth progressively decreasing to zero.

The throttle 12I and the piston I controlled thereby may assume variouspositions corresponding to various speeds of the vehicle. The fartherthe throttle I21 and piston 120 are moved to the right, the farther thepiston 117 tends to be moved to the right by the piston 120, which actsagainst piston 117 through the spring 119 and the pressure in a chamber125d formed in the cylinder 116 between pistons I17 and 120. Thepressure in chamber 125d is constant, being limited to some value suchas 200 p.s.i., because of a relief valve IZSe connected to the deliveryside of the pump 25 beyond the restriction 123. The farther the throttle121 and piston 120 are moved to the right, the greater the engine speed,the greater the speed of the pump 125, the greater the pressuredelivered by the pump 25 ahead of the restriction I23, and the greaterthe pressure in the line 122 and a chamber 126 which is connected to theline 122 and is formed between the piston I17 and the adjacent closedend of the cylinder 116. Thus, with greater engine speed and the morethe tendency for the piston 120 to move the piston 117 to the right, themore the tendency for the piston to move to the left because of thegreater difference between the greater pressure in chamber and theconstant pressure in the chamber formed between pistons 117 and 120. Sofor a given engine speed, whether high or low, and normal operation ofthe engine, the piston I17 occupies its normal position shown in FIG. 6in which position a drain line 127 leading from the cylinder 116 isblocked. In this condition, hydraulic pressure fluid flows from the line125 through the space between the reduced portion 1250 of the piston I17and the cylinder 116 and through line 27 to the direction unit 20,without escape of pressure fluid through drain line 127 and without lossof pressure from line 125 to line 27.

When, however, stalling occurs or tends to occur, the engine and thepump 25 slow down, without a change in the position of the throttle 121,and the pressure delivered by the pump 25 ahead of the restriction 123to the line 122 and the chamber 126, is reduced. Thus, the pressuredifference between chamber 126 and chamber 125d, whose pressure is heldconstant by relief valve 1250, is reduced. Because of this reducedpressure difference, the action of spring 120, and the maintenance ofposition of piston 120 by throttle 121, the piston I17 moves to theright, uncovering drain line 127 to the grooves 125!) on piston I17 andrelatively shifting the pumpdelivery line 125 from the reduced middleregion I250 of the piston 117 to he grooves 125(- thereon. Now as thehydraulic fluid flows between the piston 117 and cylinder 116 fromdelivery line 125 to drain line 127, its pressure is reduced from theconstant delivery pressure to drain pressure, because of the resistanceoffered by the grooves [25b and l25c of the piston I17.

Also, the pressure in line 27 is reduced from delivery pressure to anintermediate pressure greater than drain pressure, because of theresistance offered by the grooves I25c alone. The reduction in pressurein line 27 is dependent on the ratio of the flow resistance in groovesI2$c to the combined flow resistance in grooves 1250 and 1251). Becausegrooves 12% increase in depth from right to left as viewed in FIG. 6,and grooves decrease in depth from right to left, the more the pistonI17 moves to the right in uncovering drain line 127, the greater theresistance offered by groove 1250 and the less the resistance offered bygrooves 125b, and the more the pressure in line 27 is reduced towarddrain pressure. The more the engine slows in stalling, the lower thepressure in chamber 126, the farther the piston 117 is moved to theright, the greater the pressure reduction in line 27.

Reducing pressure in line 27 lowers the intermediate pressure in line 31or 30, line 33 or 32, and line 35 or 36, depending on whether the joystick 22 is positioned for forward or reverse, and the valves 34 and 37move the pistons 86 for a slower speed of the drive mechanisms of thevehicle. The more the pressure is reduced in line 27, the more thepistons 86 are moved, and the slower the drive mechanisms are driven.

When the engine again operates normally, its speed increases to that forwhich the throttle 121 is set, and the control pump 25 goes faster.Pressure in line 122 and chamber 126 increases, and piston 117 is movedto the left so as again to block the drain line 27. This action restoresthe pressure in line 27, and the resultant action on the lines 30, 31,32, 36, 35, and 33 makes the valves 34 and 37 reposition the pistons 86of the power units 23 and 24 for restoration of the speed of thevehicle's drive mechanisms.

It sometimes happens that the drive mechanisms do not drive the vehicleat the same speed, even though the pumps for such drive mechanisms arepresumably set through their swash plates or tilting heads for the samespeed in both drive mechanisms. Compensation for such difference inspeeds is provided by two gear pumps 128 and 129 connected to theright-hand and left-hand drive mechanisms, respectively, of the vehicle,a cylinder 130 connected to the pumps, a piston I31 mounted in thecylinder, and a rod 132 connecting the piston and the casing casingsection 56 of the steering unit 21. The gear pumps I28 and 129 arecontrolled by intake valves 133 and 134 and pressure relief valves 135and 136 operating, for example, at about 50 lbs. Chambers 137 and 138formed in the cylinder 130 at opposite sides of the piston 131 aresubjected to pressure supplied by gear pumps I28 and 129, respectively.When the drive mechanisms of the two sides of the vehicle are operatedat the same speed, the pumps I28 and 129 at the same speed, chambers 137and 138 in the cylinder 130 have the same pressure, and the piston 131is thereby centrally positioned in the cylinder 130 so as to act throughthe rod 132 to make the casing section 56 of the steering unit 21 occupya neutral or central position. When the right-hand drive mechanism ofthe vehicle has a higher speed than the left-hand drive mechanism, thegreater speed of pump 128 makes the pressure in chamber 137 greater thanthat in chamber 138. Thus, the piston 131 is moved to the right, and thecasing section and sleeve 55 of the steering unit 21 is shiftedcounterclockwise as viewed in FIG. 6. The result is that those parts arerepositioned somewhat as indicated by a comparison of FIG. 8 with FIG.7, but probably not to the extent represented by the difference betweenthese figures. The pressure in lines 32 and 33 is modified to bringabout a lower speed of the right-hand drive mechanism. At the same timethe counterclockwise shifting of the casing section 56 and sleeve 55 arewithout effect upon the lines 35 and 36 controlling the left-hand drivemechanisms, and this mechanism continues at its same speed.

Stops (not shown) are provided to limit to a small amount the movementof the piston 131 in the cylinder 130 and the angular movement of thecasing section 56 and sleeve 55 with respect to the rotor 54 of thesteering unit 21. Thus, when the vehicle is to be turned, rather thandriven in a straight direction. the angular movement of the inner memberor rotor 54 of the steering unit 21 with respect to the sleeve 55required for turning of the vehicle easily overrides the small movementof the sleeve 55 and casing section 56 permitted by the stops.

What is claimed is:

1. In a vehicle in which two drive mechanisms are driven at the samespeed in a given direction for straight forward movement of the vehicle,at the same speed in the opposite direction for straight rearwardmovement of the vehicle, and in opposite directions or at differentspeeds in the same direction for steering of the vehicle; two hydraulicactuators control the direction of drive of the drive mechanisms by thealgebraic signs of the differences of the hydraulic pressures applied tothe actuators, and the speeds of the drive mechanisms by the amountsofsaid differences; and ajoy stick is moved forwardly and rearwardly forforward and rearward movement of the vehicle and to the right and to theleft for turning of the vehicle; the combination with the actuators andthe joy stick, of

a. a direction unit having two restricted orifices of appreciablelength, each orifice having one end connected to a source of fluid underpressure and the other end con nected to drain, said unit further havingtwo take-off openings, one communicating with one orifice, the otherwith the other orifice, said unit comprising cooperating relativelymovable parts forming the two orifices between them, relative movementof the parts in one direction shifting one take-off opening along theassociated orifice in a direction toward the end connected to drain andthe other take-ofl opening along the associated orifice in a directiontoward the end connected to the source of pressure fluid, and relativemovement of the parts in the opposite direction reversing the shift ofthe take-off openings with respect to the source of pressure fluid anddrain;

b. means connecting the joy stick with the direction unit to enableforward and rearward movement of the joy stick to produce relativemovement of one of the parts of said unit in said one direction and saidother direction;

c. a steering unit comprising two cooperating relatively movable parts,two restricted orifices of appreciable length being formed betweenfacing regions of the parts, the steering unit having two supplyopenings, one being connected with one take-off opening of the directionunit, the other connected with the other take-off opening of thedirection unit, the steering unit further having first, second, third,and fourth take-off openings all formed in the same part of the steeringunit, the first and third takeoff openings being connected with onehydraulic actuator, the second and fourth take-off openings beingconnected with the other hydraulic actuator,

a central position of one steering-unit part with respect to the othercausing the first and fourth take-off openings and the second and thirdtake-off openings to be connected with the said one supply opening andthe said other supply opening, respectively, independently of theorifices in the steering unit, the first and second take-off openings tobe connected with one another by way of the entire length of the oneorifice of the steering unit, and the third and fourth take-off openingsto be connected with one another by way of the entire length of theother orifice of the steering unit,

displacement of said one steering-unit part from its central position inone direction with respect to said other steering unit part causing thefirst take-off opening and the third takeoff opening to remain connectedwith the said one supply opening and said other supply opening,respectively, independently of the orifices of the steering unit, andthe fourth take-off opening and the second take-off opening to beconnected with the said one supply opening and the said other supplyopening,

respectively, by way of portions of the lengths of the said otherorifice and the said one orifice, respectively, of the steering unit,

displacement of said one steering-unit part from its central position inthe opposite direction with respect to said other steering-unit partcausing the fourth take-off opening and the second take-off opening toremain connected with the said one supply opening and said other supplyopening, respectively, independently of the orifices of the steeringunit, and the first take-off opening and the third take-off opening tobe connected with the said one supply opening and the said other supplyopening, respectively, by way of portions of the lengths of the said oneorifice and the said other orifice, respectively, of the steering unit;and

d. means connecting the joy stick with the steering unit to enablerightward and leftward movement of the joy stick to produce relativeangular movement of the parts of the steering unit in two directions.

2. The combination as specified in claim 1,

one part of the direction unit being connected to the joy stick andbeing keyed to the said one steeringmnit part.

3. The combination as specified in claim 2, the steering unit beingformed ofinner and outer parts having facing inner and outer surfacesand being angularly movable with respect to one another about an axis ofrotation, the restricted orifices of the steering unit being formedbetween the facing surface of one of said inner and outer parts and tworelatively long grooves formed in the facing surface of the other ofsaid parts and extending for an appreciable distance generally parallelto the axis of rotation and to a slight extent about the axis ofrotation, the take-off openings of the steering unit being formed in thefacing surface of the said one part and extending parallel to said axisof rotation for an appreciable distance.

4. The combination as specified in claim 3, the grooves forming part ofthe restricted orifices of the steering unit being on the outer surfaceof the inner part, the take-off openings being formed in the innersurface of the outer part.

5. In a vehicle in which two drive mechanisms are driven at the samespeed in a given direction for straight forward movement of the vehicle,at the same speed in the opposite direction for straight rearwardmovement of the vehicle, and in opposite directions or at differentspeeds in the same direction for steering of the vehicle; twopiston-and-cylinder assemblies control the two drive mechanisms; thepiston-andcylinder assemblies are controlled by two valves, one to anassembly; and a joy stick is moved forwardly and rearwardly for forwardand rearward movement of the vehicle and to the right and to the leftfor turning of the vehicle; the combination with the valves and the joystick, of

a. a direction unit having two restricted orifices of appreciablelength, each orifice having one end connected to a source of fluid underpressure and the other end connected to drain, said unit further havingtwo take-off openings, one communicating with one orifice, the otherwith the other orifice, said unit comprising cooperating relativelymovable parts forming the two orifices between them, relative movementof the parts in one direction shifting one take-off opening along theassociated orifice in a direction toward the end connected to drain andthe other take-off opening along the associated orifice in a directiontoward the end connected to the source of pressure fluid and relativemovement in the opposite direction reversing the shift of the take-ofiopenings with respect to the source of pressure fluid and drain;

b. means connecting the joy stick with the direction unit to enableforward and rearward movement of the joy stick to produce relativemovement of one of the parts of said unit in said one direction and saidother direction, respectively;

c. a steering unit having four restricted orifices of appreciablelength, four take-off openings, and two supply openings and comprisingcooperating relatively angularly movable inner and outer parts, theorifices of the steering unit being formed between an inner surface ofthe outer part and four peripherally spaced arcuate segments of theouter surface of the inner part closely spaced from the inner surface ofthe outer part, the said four arcuate segments being spaced from oneanother by four other segments of the outer surface of the inner memberappreciably spaced from said inner surface, two of the said four othersegments being at opposite sides of the inner member and being connectedby a first opening extending through the inner member, the remaining twoof the said four other segments being at opposite sides of the innermember and being connected by a second opening in the inner memberhaving no connection with the first opening, the take-off openings beingformed in the outer member and being peripherally spaced from oneanother, the first and second of the take-off openings being spaced fromone another an amount about equal to the width of one arcuate segment ofthe exterior surface of the inner member, the third and fourth take-offopenings being spaced from one another an amount about equal to thewidth of another of the arcuate segments adjacent said one arcuatesegment, the third take-off opening being spaced from the second takeoff opening in a direction away from the first take-off opening and inan amount about equal to the width of the one of said four othersegments of the outer surface lying between said one and said otherarcuate segments, the fourth take-off opening being spaced from thethird take-off opening in the same direction as the third is spaced fromthe second, the supply openings being formed in the outer member, onebeing connected with one take-off opening in the direction unit andbeing located in generally opposed diametral relation to a region midwaybetween the second and third take-off openings, the other supply openingbeing connected with the other take-off opening in the direction unitand being spaced about 90 from one supply openmg;

d. means connecting the joy stick with the steering unit to enablecorresponding rightward and corresponding leftward movement of the joystick and steering unit.

6. The combination specified in claim 5,

the parts of the steering unit being relatively angularly movable aboutan axis of rotation and extending for an appreciable distance along theaxis of rotation,

the orifices of the steering unit being formed between the inner surfaceof the outer part and four grooves formed in the four arcuate segmentsof the outer surface on the inner part, one groove to an arcuatesegment, each groove having its ends at the sides of the associatedarcuate segments and extending for an appreciable distance generallyparallel to the axis of rotation and to a slight extent about the axisof rotation,

the four take-off openings of the steering unit being formed in theinner surface of the outer part and extending parallel to the axis ofrotation.

7. In an apparatus in which two drive mechanisms are controlled by twohydraulic actuators; the combination with the actuators, of

a hydraulic unit comprising two cooperating relatively movable parts,two restricted orifices of appreciable length being formed betweenfacing regions of the parts, the unit having two supply openings, theunit further having first, second, third, and fourth take-off openingsall formed in the same part, the first and third take-off openings beingconnected with one hydraulic actuator, the second and fourth take-offopenings being connected with the other hydraulic actuator,

a central position of one part with respect to the other causing thefirst and fourth take-off openings and the second and third take-offopenings to be connected with the said one supply opening and the saidother supply opening, respectively, independently of the orifices, thefirst and second take-off openings to be connected with one another byway of the entire length of the one orifice, and the third and fourthtake-off openings to be connected with one another by way of the entirelength of the other orifice, displacement of said one part from itscentral position in one direction with respect to said other partcausing the first take-off opening and the third take-off opening toremain connected with the said one supply opening and said other supplyopening, respectively, independently of the orifices, and the fourthtake-off opening and the second take-off opening to be connected withthe said one supply opening and the said other supply opening,respectively, by way of portions of the lengths of the said otherorifice and the said one orifice, respectively,

displacement of said one part from its central position in the oppositedirection with respect to said other part causing the fourth take-offopening and the second take-off opening to remain connected with thesaid one supply opening and said other supply opening, respectively,independently of the orifices, and the first take-off opening and thethird take-off opening to be connected with the said one supply openingand the said other supply opening, respectively, by way of portions ofthe lengths of the said one orifice and the said other orifice,respectively 8. The combination as specified in claim 7, the hydraulicunit being formed of inner and outer parts having facing inner and outersurfaces and being angularly movable with respect to one another aboutan axis of rotation, the restricted orifices being formed between thefacing surface of one of said inner and outer parts and two relativelylong grooves formed in the facing surface of the other of said parts andextending for an appreciable distance generally parallel to the axis ofrotation and to a slight extent about the axis of rotation, the takeoffopenings of the hydraulic unit being formed in the facing surface of thesaid one part and extending parallel to said axis of rotation for anappreciable distance.

9. The combination as specified in claim 8, the grooves forming part ofthe restricted orifices of the hydraulic unit being on the outer surfaceof the inner part, the take-off openings being formed in the innersurface of the outer part.

It). In an apparatus in which two drive mechanisms are controlled by twopiston-and-cylinder assemblies and said assemblies are controlled by twovalves; the combination with the valves, of

a unit having four restricted orifices of appreciable length,

four take-off openings, and two supply openings and comprisingcooperating relatively angularly movable inner and outer parts,

the orifices being formed between an inner surface of the outer part andfour peripherally spaced arcuate segments of the outer surface of theinner part closely spaced from the inner surface of the outer part,

the said four arcuate segments being spaced from one another by fourother segments of the outer surface of the inner member appreciablyspaced from said inner surface, two of the said four other segmentsbeing at opposite sides of the inner member and being connected by afirst opening extending through the inner member, the remaining two ofthe said four other segments being at opposite sides of the inner memberand being connected by a second opening in the inner member having noconnection with the first opening,

the take-off openings being formed in the outer member and beingperipherally spaced from one another, the first and second of thetake-off openings being spaced from one another an amount about equal tothe width of one arcuate segment of the exterior surface of the innermember, the third and fourth take-off openings being spaced from oneanother an amount about equal to the width of another of the arcuatesegments adjacent said one arcuate segment, the third take-off openingbeing spaced from the second take-off opening in a direction away fromthe first take-of opening and in an amount equal to the width of the oneof said four other segments of the outer surface lying between said oneand said other arcuate segments, the fourth take-off opening beingspaced from the third take-off opening in the same direction as thethird is spaced from the second,

the first and third take-off openings being connected with one valve,the second and fourth take-off openings being connected with the othervalve,

the supply openings being formed in the outer member.

1 l. The combination specified in claim it),

the parts of the unit being relatively angularly movable about an axisof rotation and extending for an appreciable distance along the axis ofrotation,

the orifices of the unit being formed between the inner surface of theouter part and four grooves formed in the four arcuate segments of theouter surface of the inner part, one groove to an arcuate segment, eachgroove having its ends at the sides of the associated arcuate segmentsand extending for an appreciable distance generally parallel to the axisof rotation and to a slight extent about the axis of rotation,

the four take-off openings of the unit being formed in the inner surfaceof the outer part and extending parallel to the axis of rotation.

12. In a vehicle in which two drive mechanisms are driven at the samespeed in a given direction for straight forward movement of the vehicle,at the same speed in the opposite direction for straight rearwardmovement of the vehicle, and at speeds in opposite directions or with aproportional differential of speed powered in the same direction forsteering of the vehicle, and in which two hydraulic actuators controlthe direction of drive of the drive mechanisms by the algebraic signs ofthe differences of the hydraulic pressures applied to the actuators, andproportionally control the speeds of the drive mechanisms by the amountsof such differences, the combination comprising:

the actuators;

a tiltable joy stick (22) and a translatory and rotary bipartite valve(20, 21) operatively related together to afford manual control over anhydraulic pressure differential applied to the actuators;

said bipartite valve having a direction part (20) with slidably relatedhydraulic differential creating elements, said actuators connected inthe output of said elements and responsive to the signs of thedifferences of the hydraulic pressures applied thereto by said elements;

said bipartite valve having a steering part (2i) with rotatably relatedhydraulic differential creating members, said actuators connected in theoutput of said members and incrementally proportionally responsive tothe amounts of differences of the hydraulic pressures applied thereto bysaid members;

means (40) supporting the joy stick and bipartite valve in the operativerelationship described enabling rightward and leftward tilt of the joystick to turn the members of the steering part in two directions ofrotation; and

means (40a, 40b) supporting the joy stick and bipartite valve in theoperative relationship described enabling forward and rearward tilt ofthe joy stick to slide the elements of the direction part in twodirections of translation.

i 1 U i

1. In a vehicle in which two drive mechanisms are driven at the samespeed in a given direction for straight forward movement of the vehicle,at the same speed in the opposite direction for straight rearwardmovement of the vehicle, and in opposite directions or at differentspeeds in the same direction for steering of the vehicle; two hydraulicactuators control the direction of drive of the drive mechanisms by thealgebraic signs of the differences of the hydraulic pressures applied tothe actuators, and the speeds of the drive mechanisms by the amounts ofsaid differences; and a joy stick is moved forwardly and rearwardly forforward and rearward movement of the vehicle and to the right and to theleft for turning of the vehicle; the combination with the actuators andthe joy stick, of a. a direction unit having two restricted orifices ofappreciable length, each orifice having one end connected to a source offluid under pressure and the other end connected to drain, said unitfurther having two take-off openings, one communicating with oneorifice, the other with the other orifice, said unit comprisingcooperating relatively movable parts forming the two orifices betweenthem, relative movement of the parts in one direction shifting onetake-off opening along the associated orifice in a direction toward theend connected to drain and the other take-off opening along theassociated orifice in a direction toward the end connected to the sourceof pressure fluid, and relative movement of the parts in the oppositedirection reversing the shift of the take-off openings with respect tothe source of pressure fluid and drain; b. means connecting the joystick with the direction unit to enable forward and rearward movement ofthe joy stick to produce relative movement of one of the parts of saidunit in said one direction and said other direction; c. a steering unitcomprising two cooperating relatively movable parts, two restrictedorifices of appreciable length being formed between facing regions ofthe parts, the steering unit having two supply openings, one beingconnected with one takeoff opening of the direction unit, the otherconnected with the other take-off opening of the direction unit, thesteering unit further having first, second, third, and fourth take-offopenings all formed in the same part of the steering unit, the first andthird take-off openings being connected with one hydraulic actuator, thesecond and fourth take-off openings being connected with the otherhydraulic actuator, a central position of one steering-unit part withrespect to the other causing the first and fourth take-off openings andthe second and third take-off openings to be connected with the said onesupply opening and the said other supply opening, respectively,independently of the orifices in the steering unit, the first and secondtake-off openings to be connected with one another by way of the entirelength of the one orifice of the steering unit, and the third and fourthtakeoff openings to be connected with one another by way of the entirelength of the other orifice of the steering unit, displacement of saidone steering-unit part from its central position in one direction withrespect to said other steering unit part causing the first take-offopening and the third take-off opening to remain connected with the saidone supply opening and said other supply opening, respectively,independently of the orifices of the steering unit, and the fourthtake-Off opening and the second take-off opening to be connected withthe said one supply opening and the said other supply opening,respectively, by way of portions of the lengths of the said otherorifice and the said one orifice, respectively, of the steering unit,displacement of said one steering-unit part from its central position inthe opposite direction with respect to said other steering-unit partcausing the fourth take-off opening and the second take-off opening toremain connected with the said one supply opening and said other supplyopening, respectively, independently of the orifices of the steeringunit, and the first take-off opening and the third take-off opening tobe connected with the said one supply opening and the said other supplyopening, respectively, by way of portions of the lengths of the said oneorifice and the said other orifice, respectively, of the steering unit;and d. means connecting the joy stick with the steering unit to enablerightward and leftward movement of the joy stick to produce relativeangular movement of the parts of the steering unit in two directions. 2.The combination as specified in claim 1, one part of the direction unitbeing connected to the joy stick and being keyed to the said onesteering-unit part.
 3. The combination as specified in claim 2, thesteering unit being formed of inner and outer parts having facing innerand outer surfaces and being angularly movable with respect to oneanother about an axis of rotation, the restricted orifices of thesteering unit being formed between the facing surface of one of saidinner and outer parts and two relatively long grooves formed in thefacing surface of the other of said parts and extending for anappreciable distance generally parallel to the axis of rotation and to aslight extent about the axis of rotation, the take-off openings of thesteering unit being formed in the facing surface of the said one partand extending parallel to said axis of rotation for an appreciabledistance.
 4. The combination as specified in claim 3, the groovesforming part of the restricted orifices of the steering unit being onthe outer surface of the inner part, the take-off openings being formedin the inner surface of the outer part.
 5. In a vehicle in which twodrive mechanisms are driven at the same speed in a given direction forstraight forward movement of the vehicle, at the same speed in theopposite direction for straight rearward movement of the vehicle, and inopposite directions or at different speeds in the same direction forsteering of the vehicle; two piston-and-cylinder assemblies control thetwo drive mechanisms; the piston-and-cylinder assemblies are controlledby two valves, one to an assembly; and a joy stick is moved forwardlyand rearwardly for forward and rearward movement of the vehicle and tothe right and to the left for turning of the vehicle; the combinationwith the valves and the joy stick, of a. a direction unit having tworestricted orifices of appreciable length, each orifice having one endconnected to a source of fluid under pressure and the other endconnected to drain, said unit further having two take-off openings, onecommunicating with one orifice, the other with the other orifice, saidunit comprising cooperating relatively movable parts forming the twoorifices between them, relative movement of the parts in one directionshifting one take-off opening along the associated orifice in adirection toward the end connected to drain and the other take-offopening along the associated orifice in a direction toward the endconnected to the source of pressure fluid and relative movement in theopposite direction reversing the shift of the take-off openings withrespect to the source of pressure fluid and drain; b. means connectingthe joy stick with the direction unit to enable forward and rearwardmovement of the joy stick to produce relative movement of one of theparts of said unit in said one direction and said other Direction,respectively; c. a steering unit having four restricted orifices ofappreciable length, four take-off openings, and two supply openings andcomprising cooperating relatively angularly movable inner and outerparts, the orifices of the steering unit being formed between an innersurface of the outer part and four peripherally spaced arcuate segmentsof the outer surface of the inner part closely spaced from the innersurface of the outer part, the said four arcuate segments being spacedfrom one another by four other segments of the outer surface of theinner member appreciably spaced from said inner surface, two of the saidfour other segments being at opposite sides of the inner member andbeing connected by a first opening extending through the inner member,the remaining two of the said four other segments being at oppositesides of the inner member and being connected by a second opening in theinner member having no connection with the first opening, the take-offopenings being formed in the outer member and being peripherally spacedfrom one another, the first and second of the take-off openings beingspaced from one another an amount about equal to the width of onearcuate segment of the exterior surface of the inner member, the thirdand fourth take-off openings being spaced from one another an amountabout equal to the width of another of the arcuate segments adjacentsaid one arcuate segment, the third take-off opening being spaced fromthe second take-off opening in a direction away from the first take-offopening and in an amount about equal to the width of the one of saidfour other segments of the outer surface lying between said one and saidother arcuate segments, the fourth take-off opening being spaced fromthe third take-off opening in the same direction as the third is spacedfrom the second, the supply openings being formed in the outer member,one being connected with one take-off opening in the direction unit andbeing located in generally opposed diametral relation to a region midwaybetween the second and third take-off openings, the other supply openingbeing connected with the other take-off opening in the direction unitand being spaced about 90* from one supply opening; d. means connectingthe joy stick with the steering unit to enable corresponding rightwardand corresponding leftward movement of the joy stick and steering unit.6. The combination specified in claim 5, the parts of the steering unitbeing relatively angularly movable about an axis of rotation andextending for an appreciable distance along the axis of rotation, theorifices of the steering unit being formed between the inner surface ofthe outer part and four grooves formed in the four arcuate segments ofthe outer surface on the inner part, one groove to an arcuate segment,each groove having its ends at the sides of the associated arcuatesegments and extending for an appreciable distance generally parallel tothe axis of rotation and to a slight extent about the axis of rotation,the four take-off openings of the steering unit being formed in theinner surface of the outer part and extending parallel to the axis ofrotation.
 7. In an apparatus in which two drive mechanisms arecontrolled by two hydraulic actuators; the combination with theactuators, of a hydraulic unit comprising two cooperating relativelymovable parts, two restricted orifices of appreciable length beingformed between facing regions of the parts, the unit having two supplyopenings, the unit further having first, second, third, and fourthtake-off openings all formed in the same part, the first and thirdtake-off openings being connected with one hydraulic actuator, thesecond and fourth take-off openings being connected with the otherhydraulic actuator, a central position of one part with respect to theother causing the first and fourth take-off openings and the second andthird take-off openings to be connected with the said one supply openIngand the said other supply opening, respectively, independently of theorifices, the first and second take-off openings to be connected withone another by way of the entire length of the one orifice, and thethird and fourth take-off openings to be connected with one another byway of the entire length of the other orifice, displacement of said onepart from its central position in one direction with respect to saidother part causing the first take-off opening and the third take-offopening to remain connected with the said one supply opening and saidother supply opening, respectively, independently of the orifices, andthe fourth take-off opening and the second take-off opening to beconnected with the said one supply opening and the said other supplyopening, respectively, by way of portions of the lengths of the saidother orifice and the said one orifice, respectively, displacement ofsaid one part from its central position in the opposite direction withrespect to said other part causing the fourth take-off opening and thesecond take-off opening to remain connected with the said one supplyopening and said other supply opening, respectively, independently ofthe orifices, and the first take-off opening and the third take-offopening to be connected with the said one supply opening and the saidother supply opening, respectively, by way of portions of the lengths ofthe said one orifice and the said other orifice, respectively.
 8. Thecombination as specified in claim 7, the hydraulic unit being formed ofinner and outer parts having facing inner and outer surfaces and beingangularly movable with respect to one another about an axis of rotation,the restricted orifices being formed between the facing surface of oneof said inner and outer parts and two relatively long grooves formed inthe facing surface of the other of said parts and extending for anappreciable distance generally parallel to the axis of rotation and to aslight extent about the axis of rotation, the take-off openings of thehydraulic unit being formed in the facing surface of the said one partand extending parallel to said axis of rotation for an appreciabledistance.
 9. The combination as specified in claim 8, the groovesforming part of the restricted orifices of the hydraulic unit being onthe outer surface of the inner part, the take-off openings being formedin the inner surface of the outer part.
 10. In an apparatus in which twodrive mechanisms are controlled by two piston-and-cylinder assembliesand said assemblies are controlled by two valves; the combination withthe valves, of a unit having four restricted orifices of appreciablelength, four take-off openings, and two supply openings and comprisingcooperating relatively angularly movable inner and outer parts, theorifices being formed between an inner surface of the outer part andfour peripherally spaced arcuate segments of the outer surface of theinner part closely spaced from the inner surface of the outer part, thesaid four arcuate segments being spaced from one another by four othersegments of the outer surface of the inner member appreciably spacedfrom said inner surface, two of the said four other segments being atopposite sides of the inner member and being connected by a firstopening extending through the inner member, the remaining two of thesaid four other segments being at opposite sides of the inner member andbeing connected by a second opening in the inner member having noconnection with the first opening, the take-off openings being formed inthe outer member and being peripherally spaced from one another, thefirst and second of the take-off openings being spaced from one anotheran amount about equal to the width of one arcuate segment of theexterior surface of the inner member, the third and fourth take-offopenings being spaced from one another an amount about equal to thewidth of another of the arcuate segments adjacent said one arcuatesegment, the third take-off opeNing being spaced from the secondtake-off opening in a direction away from the first take-of opening andin an amount equal to the width of the one of said four other segmentsof the outer surface lying between said one and said other arcuatesegments, the fourth take-off opening being spaced from the thirdtake-off opening in the same direction as the third is spaced from thesecond, the first and third take-off openings being connected with onevalve, the second and fourth take-off openings being connected with theother valve, the supply openings being formed in the outer member. 11.The combination specified in claim 10, the parts of the unit beingrelatively angularly movable about an axis of rotation and extending foran appreciable distance along the axis of rotation, the orifices of theunit being formed between the inner surface of the outer part and fourgrooves formed in the four arcuate segments of the outer surface of theinner part, one groove to an arcuate segment, each groove having itsends at the sides of the associated arcuate segments and extending foran appreciable distance generally parallel to the axis of rotation andto a slight extent about the axis of rotation, the four take-offopenings of the unit being formed in the inner surface of the outer partand extending parallel to the axis of rotation.
 12. In a vehicle inwhich two drive mechanisms are driven at the same speed in a givendirection for straight forward movement of the vehicle, at the samespeed in the opposite direction for straight rearward movement of thevehicle, and at speeds in opposite directions or with a proportionaldifferential of speed powered in the same direction for steering of thevehicle, and in which two hydraulic actuators control the direction ofdrive of the drive mechanisms by the algebraic signs of the differencesof the hydraulic pressures applied to the actuators, and proportionallycontrol the speeds of the drive mechanisms by the amounts of suchdifferences, the combination comprising: the actuators; a tiltable joystick (22) and a translatory and rotary bipartite valve (20, 21)operatively related together to afford manual control over an hydraulicpressure differential applied to the actuators; said bipartite valvehaving a direction part (20) with slidably related hydraulicdifferential creating elements, said actuators connected in the outputof said elements and responsive to the signs of the differences of thehydraulic pressures applied thereto by said elements; said bipartitevalve having a steering part (21) with rotatably related hydraulicdifferential creating members, said actuators connected in the output ofsaid members and incrementally proportionally responsive to the amountsof differences of the hydraulic pressures applied thereto by saidmembers; means (40) supporting the joy stick and bipartite valve in theoperative relationship described enabling rightward and leftward tilt ofthe joy stick to turn the members of the steering part in two directionsof rotation; and means (40a, 40b) supporting the joy stick and bipartitevalve in the operative relationship described enabling forward andrearward tilt of the joy stick to slide the elements of the directionpart in two directions of translation.